Damping and sealing system for turbine blades

ABSTRACT

With a gas-turbine engine, a sealing and damping element ( 9 ), which is loosely held between two adjacent platforms ( 6   a   , 6   b ) of turbine blades attached to a rotor disk, generally has a cross-section in the form of a straight three sided prism corresponding to an equilateral triangle, however with convex rubbing surface sides. Due to small swiveling movements enabled by the curvature of the sides, an increased rubbing and wear area is created during operation, which is adapted to the blade geometry and can be determined in advance, thus increasing damping and sealing efficiency.

This application claims priority to German Patent Application DE 10 2006041 322.9 filed Sep. 1, 2006, the entirety of which is incorporated byreference herein.

This invention relates to a damping and sealing system for turbineblades with a sealing and damping element generally in the form of astraight three sided prism with equal sides which, by centrifugaleffect, is retained between opposite faces of adjacent platforms of theblades fitted to the rotor of a gas-turbine engine.

Gas-turbine engines feature rotor disks with radially extending blades,having a blade root, a platform and an airfoil, mounted on the peripheryof the rotor disks. On the one hand, there is a need to seal the narrowgap remaining between adjoining edges of adjacent platforms to minimizegas exchange between hot gas and cooling air; on the other hand, it isnecessary to dampen the vibrations between the rotor disk and theblades, as well as between the blades themselves.

Sealing elements arranged between the blade platforms have been longknown, whose cross-section is complementary to the shape of the spaceremaining between the platforms and which must be installed in thisspace in a specific orientation. Assembly is accordingly time-consumingand costly, and incorrect orientation of the sealing elementconsiderably affects its sealing and damping efficiency. Moreover, theclosely matched form of sealing element and platform gap requiresconsiderable production effort.

For one solution to this problem, Specification U.S. Pat. No. 4,872,812proposes a sealing and damping element with planar sides arranged aboutits longitudinal axis, with the cross-section of this sealing anddamping element being an equilateral triangle. The regular cross-sectionof the sealing and damping element enables two each of its surfaces,irrespective of the orientation with which the element is assembled, tobe driven into engagement with the respective edges of the adjacentplatforms to seal the gap and dampen the vibrations of the respectiveblades when acted upon by centrifugal force. High sealing and dampingefficiency requires, however, close production tolerances and, thus highproduction effort with regard to the planar form of the mating surfaceson both sides. Moreover, the sealing and damping efficiency can beaffected by wear to the planar mating surfaces.

In order to reduce the production and assembly effort, sealing anddamping elements with circular cross-section have been proposed which,in any orientation, mate with the side edges of the two adjacentplatforms when acted upon by centrifugal force. It was found, however,that round sealing and damping elements wear quite rapidly, as a resultof which the sealing and damping efficiency is affected and the sealingand damping elements have to be replaced with considerable effort.

In a broad aspect, the present invention provides a sealing and dampingsystem for turbine blades, which is characterized by a high sealing anddamping efficiency, while requiring only low assembly and repair effort.

It is a particular object of the present invention to provide at leastone solution to the above problems by a sealing and damping systemdesigned in accordance with the features described herein. Advantageousdevelopments of the present invention become apparent from the presentdescription.

The present invention provides a sealing and damping element in the formof a straight three sided prism with convex sides allowing the sealingand damping element to perform a slight swiveling movement in operationand thus acting as enlarged rubbing surfaces. The increased frictionthus obtained results in improved vibration damping. Rubbing wear leadsto a mutual conditioning of the contacting mating surfaces. Thus,production tolerances are leveled out and vibration damping and sealingefficiency is further improved. Production inaccuracies are compensatedfor by the automatic, mutual conditioning of the sealing or rubbingsurfaces. Rubbing wear can be taken into account in the design.Therefore, the production and repair effort is low.

The opposite sealing surfaces of the adjacent blade platforms form anacute-angled gap into which the sealing and damping element isautomatically forced by the action of centrifugal force, contacting thegap surfaces with two curved rubbing surfaces.

The present invention is more fully described in light of theaccompanying drawings. In the drawings,

FIG. 1 is a partial view of a gas turbine with a turbine blade attachedto a rotor disk, and

FIG. 2 is a section AA as per FIG. 1 with a sealing and damping elementarranged between two blades.

As can be seen from FIG. 1, a rotor 2 is disposed between two statorvanes 1 spaced in flow direction, with turbine blades 4 arranged on theperiphery of a rotor disk 3, which includes a blade root 5, a bladeplatform 6 and an airfoil 7. The detailed representation in FIG. 2 showstwo adjoining platforms 6 a, 6 b of adjacent turbine blades 4. Theplatform 6 a, shown on the right-hand side of the drawing, features arecess 8 in which a sealing and damping element 9 is loosely received.Positioned opposite to the open side of the recess 8—with a very smallgap 10 left—is a planar, essentially vertical platform edge 11 of theother platform 6 b which prevents the sealing and damping element 9 fromfalling out of the recess 8. The recess 8 has a sealing surface 12 whichextends obliquely upwards. The sealing and damping element 9 is astraight component with the cross-section generally of an equilateraltriangle, however with rounded longitudinal edges 13 and withconvex—crowned—rubbing surfaces 14 (sealing and damping faces, sidefaces) between the longitudinal edges 13. One of the edges 13 facesgenerally upward, as shown in FIG. 2.

The sealing and damping element 9 is loose in the recess 8 at rest.During rotation of the rotor 2, however, centrifugal force acts on thesealing and damping element 9 so that its respective convex rubbingsurfaces 14 abut the vertical platform edge 11 and the oblique sealingsurface 12. Rotation of the sealing and damping element 9 about itslongitudinal axis is thus counteracted. However, the curvature and therotationally symmetric arrangement of the curved rubbing surfaces 14about a longitudinal axis allow the sealing and damping element 9 toperform a slight swiveling movement about the longitudinal axis, inconsequence of which the curved rubbing surfaces 14 are conditioned, andslightly flattened, by wear in the areas of contact with the platformedge 11 and the oblique sealing surface 12, so that the actual area ofrub is increased and adapted to the platform design, and geometricaldifferences caused by the production process are leveled out. Inaddition, the slight swiveling movement which the sealing and dampeningelement is allowed to perform enlarges the area of rub and increasesfriction. The deliberately effected wear due to friction of the curvedrubbing surfaces 14 and the mating surfaces with the two oppositeplatforms is determinable in advance, and is accounted for in the bladedesign. By interaction of the above effects, an optimum rubbing surfaceis provided and, due to high friction, maximum damping and, ultimately,improved sealing efficiency achieved, but with the sealing and dampingelement being prevented from uncontrolled or premature wear by permanentrotation. The production and repair effort is reduced.

LIST OF REFERENCE NUMERALS

-   1 Stator vane-   2 Rotor-   3 Rotor disk-   4 Turbine blades-   5 Blade root-   6 Platform-   6 a Right-hand platform-   6 b Left-hand platform-   7 Airfoil-   8 Recess-   9 Sealing and damping element-   10 Gap-   11 Straight, vertical platform edge-   12 Oblique sealing surface-   13 Rounded longitudinal edges-   14 Rubbing surface, curved side face

1. A damping and sealing system for turbine blades of a gas-turbineengine, comprising: a sealing and damping element generally in the formof a straight three sided prism with equal side faces which, bycentrifugal effect during operation of the gas-turbine engine, isretained between opposing surfaces of adjacent platforms of the bladesfitted to a rotor of the gas-turbine engine, wherein the side faces ofthe sealing and damping element are configured as convex rubbingsurfaces to allow for a slight swiveling movement of the rubbingsurfaces with respect to the opposing surfaces of the adjacent bladeplatforms to thereby increase rubbing efficiency.
 2. A damping andsealing system in accordance with claim 1, wherein the opposing surfacesof the adjacent platforms form a wedge-shaped, acute-angled gap, inwhich the sealing and damping element is loosely fixed.
 3. A damping andsealing system in accordance with claim 2, wherein the gap is formed bya generally straight platform edge of the one platform and by an obliquesealing surface in a recess of the other platform.
 4. A damping andsealing system in accordance with claim 3, wherein the gap surfaces inthe rubbing/wear area of the sealing and damping element are dimensionedin a manner commensurate with an amount of wear expected.
 5. A dampingand sealing system in accordance with claim 4, wherein longitudinaledges of the sealing and damping element are rounded.
 6. A damping andsealing system in accordance with claim 1, wherein longitudinal edges ofthe sealing and damping element are rounded.